The present invention relates to a developer carrier, a developing device used for a copier, a facsimile, a printer and so on, and a process cartridge, an image forming apparatus, and an image forming method using therefor.
Generally, in a developing device using a two-component developer, a developing sleeve (developer roller) with a rough surface is used as a developer carrier. As methods of forming the rough surface of the developer roller, a blasting process, such as a sandblasting and so on, which roughens a surface and forms an irregular fine rough surface, and a grooving process, which cuts a cyclic groove on a surface, are practically used.
In the developer roller by the blasting process, compared with the developer roller by the grooving process, a cyclic unevenness in a distribution of the developer seldom occurs and the distribution is uniform, and thereby a picture quality is generally excellent. However, with a long-time use, a fine roughness on the surface is abraded and degraded. Accordingly, a carrying ability of the developer is degraded, a developer carried to a developing area is reduced with time, and a problem of a degradation of a density or an unevenness of the density may occur. On the other hand, in the developer roller by the grooving process, a degradation of the roughness on the surface with time is small; therefore the carrying ability of the developer is stable.
As for the grooving process, as illustrated in FIGS. 4 and 5, a linear v-shape groove, in which a triangle-shape cross-section is cyclically cut parallel to an axis of the developer roller on the surface of the developer roller, is widely used. However, in the linear v-shape groove, a uniformity of the distribution of the developer is degraded by an unevenness of carrying the developer corresponding to a groove pitch. And therefore, an unevenness of a pitch corresponding to the groove pitch in a circumferential direction and a degradation of a dot reproducibility may occur. In addition, the linear v-shape groove is formed perpendicularly to a carrying direction of the developer; therefore it is hard for the developer to move in an axis direction while being carried to the developing area. If it is hard for the developer to move in the axis direction, the developer is carried to the developing area in a state of having a subtle unevenness in regard to the axis direction in a case of being held by the developer roller, and the unevenness of the density in regard to the axis direction and the degradation of the dot reproducibility may occur. Thus, in the developer roller by the grooving process, in order to prevent the degradation of the picture quality by the unevenness of the density of an image and the degradation of the dot reproducibility, improving the uniformity of the distribution of the developer on the developer roller is required.
On the other hand, various kinds of shape of a groove on the surface of the developer roller have been proposed. For example, as illustrated in FIG. 6, Japanese patent publication number S60-256170 discloses that a diagonal groove which is inclined in one direction to the axis is formed uniformly in the circumferential direction. In the diagonal groove, the unevenness of carrying the developer corresponding to the groove pitch in regard to the circumferential direction is prevented, and since the developer is also moveable in the axis direction when the developer is carried, the uniformity of the distribution of the developer is improved. However, since the groove is inclined to the one direction to the axis, the developer receives a force in one side direction to the axis and may lean to one side end. In the one side end where the developer leans, a density rise or a stress of the developer is increased, and in the other side end, a degradation of the density or a cyclic unevenness is easily conspicuous.
Additionally, as illustrated in FIG. 7, for example, Japanese patent publication numbers 2000-242073 and 2003-208012 disclose a diagonal grid groove where a gird interval is formed uniformly on a surface. In the diagonal grid groove, grooves are criss-crossed, and thereby the developer does not lean to the one side on the developer roller and the uniformity of the distribution is improved.
However, in the diagonal grid groove, there are intersections of the groove, and at the intersections, an unevenness of the density of the image, such as a vertical white stripe which is called an unevenness of an intersection, may newly occur.